Make stroke.c standards-compliant

Alright, clang you win. This sacrifices readability for portability,
and if you can't use nested functions, you end up with functions
with 13 parameters...
Port to gtk3
Do tooltips right
Add an app menu
update .gitignore
Improve autostart
Reenable proximity for supported devices

I'm not aware of any drivers that support this as of now
make activate() function static
Refactor event handling code
Remove some dead code
Improve X error messages